The invention relates to nonwoven fabric and to a method and apparatus for the production of same.
Nonwoven fabrics and various methods and apparatus for their production are well known in the art. For example, the original nonwoven fabric, wool felt, is as old as any textile. However, in the last ten to fifteen years, synthetic materials have become very important in the nonwoven industry. One of the more common methods used to produce nonwoven fabrics from a batt of synthetic materials such as polypropylene, involves simply needling the batt, which is well known in the art. The needled batt is frequently bonded on one or both sides subsequent to the needling operation, depending upon the properties desired in the final product. Various bonding techniques are also well known.
There are several ways of producing the batt prior to needling and bonding. The first and simplest method is to place several carding machines (or cards) in series, laying the web produced on each successive card on top of the web produced on the preceding card. This method produces a batt with fibers oriented primarily in the longitudinal (warp) direction and thus the nonwoven fabric has much less dimensional stability in the transverse (fill) direction than in the warp direction. As used herein the term "dimensional stability" means the ability of a nonwoven fabric to resist deformation in the warp and/or fill directions due to stresses experienced by the fabric. Improved dimensional stability is indicated by an increase in tear strength and a decrease in percent elongation.
The second method used to produce a batt is that of crosslapping whereby a batt of suitable weight is built by layering a web from a card back and forth on a moving conveyor, such as a floor apron. The fabric produced by such a card and a crosslapper primarily has fibers crosswise in the finished fabric, thus the nonwoven fabric has much less dimensional stability in the warp direction than in the fill direction. Frequently it is necessary to increase the strength of the batt in the warp direction before the batt will process through the needle loom. The lack of sufficient warp strength to process is particularly acute for nonwoven fabrics having a weight of less than about 5 ounces per square yard. As a result, additional strength is often provided by the use of warp threads which are threads of polyester staple or other suitable material spaced 1/4-inch or so apart along the bottom surface of the batt, and running parallel to the warp direction of the batt. Although the use of warp threads has proven to produce a useful product, warp threads, of course, increase the overall cost of the fabric. In addition there is room for improvement of the dimensional stability in the warp direction as compared to the dimensional stability in the fill direction.
A third method used to produce a batt is a combination of the first two methods, that is, laying one or more webs in the warp direction by use of one or more cards and laying one or more additional webs in the fill direction by use of a crosslapper. This method produces a product having a better distribution of dimensional stability between the warp and fill directions; however, the dimensional stability is relatively low and a substantially greater initial investment in equipment is required than with either of the two methods previously described.
Therefore, it is an object of the invention to produce a nonwoven fabric.
Another object of the invention is to produce a nonwoven fabric of synthetic fibers.
Still another object of the invention is to produce a nonwoven fabric of synthetic fibers.
Still another object of the invention is to produce a nonwoven fabric by crosslapping without the use of warp threads.
Still another object of the invention is to produce a nonwoven fabric without the use of warp threads but possessing a relatively high dimensional stability in the warp direction.
Still another object of the invention is to provide apparatus suitable for the production of nonwoven fabrics.
Other objects, aspects and advantages of the present invention will be more apparent to one skilled in the art after studying the specification, drawings and the appended claims.